Press brakes used to shape sheet material, such as sheet metal or the like, commonly include a lower table and an upper table. Typically, at least one of these tables is vertically movable toward the other table. In most cases, the upper table is movable while the lower table remains fixed. Forming means are mounted to each table so that when the tables are brought together, a workpiece between them is bent into the desired shape.
It is common for the upper table to include a male forming tool having a downwardly-oriented, generally V-shaped bottom surface that is configured according to the particular shape into which workpieces will be deformed, and which is received in the V-shaped recess of a die carried by the lower table. Thus, when the tables are brought together, a workpiece between the two is pressed by the forming tool into the die to deform the workpiece into the desired shape. The forming tools and dies commonly are horizontally elongated so that workpieces of various widths can be accommodated. In order to accurately deform workpieces, it is necessary that the forming tool and its respective die be precisely aligned with one another during use.
Various press brake tool holders have been devised to mount a forming tool to an upper table. For example, U.S. Pat. No. 5,782,308 discloses a tool holder with a clamping plate that is pivotally attached to a stationary support plate. During use, a surface of the clamping plate exerts a clamping pressure upon the shank of a forming tool. To keep the tool from falling when the clamping force is released, the clamping plate is provided with an engagement strip that is pretensioned to engage a complementary groove in the tool shank.
The ability of existing press brake tool holders to securely hold forming tools could be improved upon. In many cases, more substantial clamping forces would be beneficial in holding the forming tool in place. Existing tool holders may provide a clamping force that is substantial in the horizontal direction. However, known tool holders commonly fail to provide a clamping force that is substantial in the vertical direction. As a result, unintentional movements of the forming tool can occur during use. As discussed above, this can result in imprecisely deformed workpieces.
It is also important, of course, that the forming tool be easily removed and replaced. It frequently becomes necessary to exchange forming tools and dies in order to accommodate a different bending operation. The dies, commonly resting on the bottom table of a press brake, are readily removed and exchanged for others. On the other hand, the forming tools, which are normally mounted to the upper table of a press brake, tend not to be so easily replaced. The forming tool is often held by a C clamp or a similar holder to the horizontally elongated bed of the upper table.
In some instances, the forming tool can only be removed by sliding it horizontally from the clamp. In other instances, the forming tool can be removed downwardly once the clamp has been loosened. Both removal methods can have drawbacks. In instances where the forming tool is removed by sliding it horizontally from the clamp, removal can be difficult if a long tool must be replaced. The proximity of neighboring clamps and tools can make it difficult to slide the tool from its clamp. The removal of forming tools can also be difficult in instances where a particular tool is removed downwardly. Long forming tools can be quite heavy. When a clamp is loosened to the point where a tool can be removed by moving it downward, the tool may slip and fall.
Tool holders can also be used advantageously as fixtures for tool testing. In this case, one or more forming tools are held in an upwardly-oriented position and are tested to assure each tool is correctly and precisely shaped. For example, a number of aligned forming tools can be easily checked for consistency by assessing whether the forming edges and other surfaces of adjacent tools are precisely aligned with one another. Tool holders may be used in a similar manner to hold forming tools while they are reworked or reconditioned.
A variety of different forming tools can be used with existing press brakes. The forming edge of each tool will vary according to the particular bending operation for which that tool was designed. Furthermore, while the narrow mounting shanks of existing tools tend to have standardized dimensions, slight variations sometimes exist in the dimensions of individual shanks. Such variations can affect the fit of the tool in the tool holder. Accordingly, a tool holder that can accommodate minor variations in tool shank dimension is desirable. Optimally, such a tool holder would be self-adjusting to the shank of each forming tool.